We propose to study the independent and combined effects of 9 months of endurance exercise training and hormone replacement therapy (HRT) on left ventricular (LV) size and function on arterial stiffness in 60 to 72 yr- old women. Maximal cardiac output will be measured by the acetylene rebreathing procedure. LV size and function will be assessed by 2-d echocardiography and Doppler ultrasound under basal conditions and during alpha and beta adrenergic stimulation induced by phenylephrine and isoproterenol, respectively.